Auxiliary commutated silicon-controlled rectifier circuit methods and systems

ABSTRACT

An illustrative device includes a first silicon-controlled rectifier (SCR) and a second silicon-controlled rectifier (SCR) connected in anti-parallel and a first commutation module, which includes a first voltage source, a first diode, and a first self-commutating semiconductor switch. The device also includes a second commutation module including a second voltage source, a second diode, and a second self-commutating semiconductor switch. The first voltage source, the first diode, and the first self-commutating semiconductor switch of the first commutation module are connected in series. The second voltage source, the second diode, and the second self-commutating semiconductor switch of the second commutation module are connected in series. The first SCR, the second SCR, the first commutation module, and the second commutation module are connected in parallel. The commutation modules are configured to apply reverse bias voltages to the first and second SCRs to turn off the SCRs.

BACKGROUND

An electrical load which receives power through an AC power system isgenerally designed to operate reliably when the actual supply inputvoltage is within approximately 10% of the rated supply input voltage. Avoltage sag (or dip) can refer to a temporary reduction of the rms ACvoltage in which the actual supply input voltage is below approximately90% of the rated supply input voltage. A dynamic voltage sag correctiondevice can refer to a device which is capable of correcting temporaryvoltage sags in a voltage input signal that is being provided to a load.Voltage sags can be caused by startup of a large load within a facility,a circuit fault, a fault on the utility transmission or distributionsystem, a problem with a generator, or any of a number of other reasons.The dynamic voltage sag correction device is generally inserted betweenthe voltage input and the load, and includes a combination of circuitelements and logic which are adapted to provide a correction signalalmost instantaneously. A dynamic voltage sag correction device is onetype of device that may utilize a static switch. A static switch may beused in a dynamic voltage sag correction device to switch between asupply input voltage and a correction signal.

SUMMARY

An illustrative device includes a silicon-controlled rectifier (SCR) anda commutation module including a voltage source, a first diode, and aself-commutating semiconductor switch. The voltage source, the firstdiode, and the self-commutating semiconductor switch of the commutationmodule are connected in series. The SCR is connected in parallel to thecommutation module. The commutation module is configured to apply areverse bias voltage to the SCR to turn it off.

An illustrative method includes connecting a silicon-controlledrectifier (SCR) and a commutation module in parallel. The commutationmodule includes a voltage source, a first diode, and a self-commutatingsemiconductor switch connected in series. The method further includesconnecting a load to an operating signal. The method further includespassing the operating signal through the SCR to the load. The methodfurther includes applying, by the commutation module, a reverse biasvoltage to the SCR to turn off the SCR.

Another illustrative device includes a first silicon-controlledrectifier (SCR) and a second silicon-controlled rectifier (SCR)connected in anti-parallel and a first commutation module, whichincludes a first voltage source, a first diode, and a firstself-commutating semiconductor switch. The device also includes a secondcommutation module including a second voltage source, a second diode,and a second self-commutating semiconductor switch. The first voltagesource, the first diode, and the first self-commutating semiconductorswitch of the first commutation module are connected in series. Thesecond voltage source, the second diode, and the second self-commutatingsemiconductor switch of the second commutation module are connected inseries. The first SCR, the second SCR, the first commutation module, andthe second commutation module are connected in parallel. The firstcommutation module is configured to apply a first reverse bias voltageto the first SCR to turn off the first SCR, and the second commutationmodule is configured to apply a second reverse bias voltage to thesecond SCR to turn off the second SCR.

Another illustrative device includes a first silicon-controlledrectifier (SCR) and a second silicon-controlled rectifier (SCR)connected in anti-parallel. The device further includes a commutationmodule connected in parallel with the first SCR and the second SCR. Thecommutation module includes a first terminal on a supply side of thedevice connected to an anode side of a third silicon-controlledrectifier (SCR) and a cathode side of a fourth silicon-controlledrectifier (SCR). The commutation module further includes a secondterminal on a load side of the device connected to an anode side of afifth silicon-controlled rectifier (SCR) and a cathode side of a sixthsilicon-controlled rectifier (SCR). The commutation module furtherincludes a third terminal connected to a cathode side of the third SCR,a cathode side of the fifth SCR, and a first side of a self-commutatingsemiconductor switch. The commutation module further includes a fourthterminal connected to an anode side of the fourth SCR, an anode side ofthe sixth SCR, and a first side of a voltage source. The commutationmodule further includes a fifth terminal connected to a second side ofthe self-commutating semiconductor switch and a second side of thevoltage source.

Another illustrative method includes connecting an alternating current(AC) static switch and a commutation module in parallel. The AC staticswitch includes a first silicon-controlled rectifier (SCR) and a secondsilicon-controlled rectifier (SCR) connected in anti-parallel. Themethod further includes connecting a load to an operating signal throughthe AC static switch during a normal operating condition. The AC staticswitch is in a closed position during the normal operating condition.The method further includes detecting, by a controller, a voltage sag orvoltage swell. The method further includes applying a reverse biasvoltage to the first SCR or the second SCR of the AC static switch. TheAC static switch is in an open position during at least a portion of thevoltage sag or voltage swell. The reverse bias voltage turns off thefirst SCR or the second SCR.

Another illustrative method includes applying a Normal_On signal to analternating current (AC) static switch comprising a firstsilicon-controlled rectifier (SCR) and a second silicon-controlledrectifier (SCR) connected in anti-parallel. The first SCR and the secondSCR are turned on. The method further includes detecting a voltage sagor voltage swell in an operating signal passing through the AC staticswitch, wherein the operating signal is an alternating current signal.The method further includes removing the Normal_On signal from the firstSCR and the second SCR in response to detecting the voltage sag orvoltage swell. The method further includes applying a first reverse biasvoltage to the first SCR when a positive current is flowing through thefirst SCR. The method further includes applying a second reverse biasvoltage to the second SCR when a negative current is flowing through thesecond SCR.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments will hereafter be described with reference tothe accompanying drawings.

FIG. 1 is a circuit diagram illustrating an auxiliary commutatedsilicon-controlled rectifier (SCR) in accordance with an illustrativeembodiment.

FIG. 2 is a circuit diagram illustrating an auxiliary commutated SCRwith an insulated-gate bipolar transistor (IGBT) and a control and gatedrive in accordance with an illustrative embodiment.

FIG. 3A is a circuit diagram illustrating a full alternating current(AC) switch utilizing SCRs and IGBTs in accordance with an illustrativeembodiment.

FIG. 3B is a circuit diagram illustrating a full alternating current(AC) switch utilizing paired self-commutating semiconductor switches anddiodes in accordance with an illustrative embodiment.

FIG. 4 is a circuit diagram illustrating an AC switch utilizing snubbercomponents in accordance with an illustrative embodiment.

FIG. 5A is a circuit diagram illustrating an AC switch utilizing abi-directional voltage clamp in accordance with an illustrativeembodiment.

FIG. 5B is a circuit diagram illustrating an alternative embodiment ofan AC switch utilizing an isolated bi-directional voltage clamp inaccordance with an illustrative embodiment.

FIG. 6 is a circuit diagram illustrating a fully integrated AC switchwith a shunt connected inverter and input rectifier in accordance withan illustrative embodiment.

FIG. 7A is a circuit diagram illustrating an auxiliary commutatedalternating current (AC) static switch circuit with only one IGBT andfour auxiliary SCRs in accordance with an illustrative embodiment.

FIG. 7B is a circuit diagram illustrating an alternative auxiliarycommutated alternating current (AC) static switch circuit with only oneIGBT and four auxiliary SCRs in accordance with an illustrativeembodiment.

FIG. 8 is a graph illustrating simulated voltage results of an auxiliarycommutated SCR circuit without a voltage clamp in accordance with anillustrative embodiment.

FIG. 9 is a graph illustrating simulated current results of an auxiliarycommutated SCR circuit without a voltage clamp in accordance with anillustrative embodiment.

FIG. 10 is a graph illustrating laboratory results of an auxiliarycommutated SCR circuit without a voltage clamp in accordance with anillustrative embodiment.

FIG. 11 is a graph illustrating simulated voltage results of anauxiliary commutated SCR circuit with a voltage clamp in accordance withan illustrative embodiment.

FIG. 12 is a graph illustrating simulated current results of anauxiliary commutated SCR circuit with a voltage clamp in accordance withan illustrative embodiment.

FIG. 13 is a graph illustrating laboratory results of an auxiliarycommutated SCR circuit with a voltage clamp in accordance with anillustrative embodiment.

FIG. 14 is a circuit diagram illustrating feedback elements of anauxiliary commutated SCR circuit control in accordance with anillustrative embodiment.

FIG. 15 is a flow chart illustrating an auxiliary commutated SCR circuitcontrol process in accordance with an illustrative embodiment.

FIG. 16 is a circuit diagram illustrating a dynamic brake for anauxiliary commutated SCR circuit in accordance with an illustrativeembodiment.

DETAILED DESCRIPTION

Disclosed herein are illustrative systems and methods for a staticswitch used, for example, in voltage sag or voltage swell correctiondevices. Static switches disclosed herein can include thyristors such assilicon-controlled rectifiers (SCR).

Advantageously, SCR devices used in static switches as disclosed hereinmay be used in many different applications. As just one example, staticswitches with SCRs may be used in voltage sag or voltage swellcorrection devices, including single phase and three (3) phase DynamicSag Corrector (DySC) devices. Such devices may be rugged, low cost, havehigh surge capabilities, and have a low loss. For an illustrativeexample of a DySC device, see U.S. Pat. No. 7,920,392, which isincorporated herein by reference in its entirety.

Other uses of a static switch are also contemplated. In an illustrativeembodiment, a static switch as disclosed herein may be used anywhere adirect current (DC) or alternating current (AC) static switch may beused. For example, an AC static switch as disclosed herein may be usedas a transfer switch to switch a load between multiple sources.Similarly, a static switch may be used to switch quickly between powersources where an uninterruptible power supply (UPS) is used. In anotherexample, the static switches disclosed herein may be used in anautomatic voltage regulator.

In an illustrative embodiment, a static switch as disclosed herein maybe used to switch between sources in a dual feed power system. A dualfeed power system may also, in some embodiments, utilize a voltage sagor voltage swell corrector. In such an embodiment, a static switch maybe used to quickly switch between the dual feeds if a problem (such as avoltage sag or voltage swell or outage) is detected with one of thesources. For an illustrative example of a dual source DySC device, seeU.S. Pat. No. 7,129,599, which is incorporated herein by reference inits entirety.

Such static switch applications may, as disclosed herein, utilize acircuit to commutate the SCRs. That is, when SCRs are used as a switch,circuit components can be used as disclosed herein to force commutatethe SCRs off. The SCRs can remain on and prevent optimal functioning ofa static switch if the SCRs are not commutated off quickly. In otherwords, an SCR may be turned on (thus a static switch is on or closed) byapplying a signal to the gate of the SCR, but the SCR may functionallyremain on even if the gate signal applied to the SCR is removed.Accordingly, an auxiliary commutation circuit as disclosed herein may beutilized to turn off an SCR (and subsequently a static switch with anSCR). In order to commutate an SCR off, current through the SCR shouldbe forced to zero by applying a reverse bias voltage to the SCR.Accordingly, in an example where static switches are used in a voltagesag or voltage swell correction device, the device may detect a sag inan operating signal, and the device can commutate a static switch (i.e.,the SCRs used in the static switch) off, which allows the device todisconnect the operating signal and apply a correction signal to correctthe sag.

FIG. 1 is a circuit diagram illustrating an auxiliary commutatedsilicon-controlled rectifier (SCR) in accordance with an illustrativeembodiment. In alternative embodiments, fewer, additional, and/ordifferent elements may be present. The auxiliary commutated SCR circuitin FIG. 1 shows a commutating device that can momentarily divert currentfrom an SCR to turn it off.

FIG. 1 includes an input terminal 115 and an output terminal 110. FIG. 1also includes a voltage source 125, a self-commutating semiconductorswitch 120, and an SCR 105. The voltage source 125 and theself-commutating semiconductor switch 120 are connected in series. Thevoltage source 125 is connected to the input terminal 115, while theself-commutating semiconductor switch 120 is connected to the outputterminal 110. The SCR 105 is connected to the input terminal 115 and theoutput terminal 110, as well as being connected in parallel with thevoltage source 125 and the self-commutating semiconductor switch 120.

In order to commutate the SCR 105 (turn it off), a first gate currentmust be removed from the SCR 105, then the self-commutatingsemiconductor switch 120 can be pulsed on to apply a reverse biasvoltage to the SCR 105 from the voltage source 125 for at least thelength of the SCR 105's turn-off time. In this way, the SCR 105 can beadequately turned off when desired. In one illustrative embodiment, aswitched current source may be connected to the SCR 105 gate in order toturn it on and off.

FIG. 2 is a circuit diagram illustrating an auxiliary commutated SCRwith an insulated-gate bipolar transistor (IGBT) and a control and gatedrive 250 in accordance with an illustrative embodiment. The IGBT ofFIG. 2 is a type of self-commutated transistor device. In alternativeembodiments, fewer, additional, and/or different elements may bepresent. A circuit 200 in FIG. 2 shows an SCR 205, a capacitor 240, afirst diode 235, and a self-commutating semiconductor switch 220. Theself-commutating semiconductor switch 220, the diode 235, and thecapacitor 240 are connected in series, as well as to an input terminal215 and an output terminal 210. The SCR 205 is connected to the inputterminal 215 and the output terminal 210, and is also connected inparallel with the series string comprising capacitor 240, the firstdiode 235, and the self-commutating semiconductor switch 220. Theself-commutating semiconductor switch 220 includes a self-commutatingtransistor device (IGBT) 225 and a second diode 230. Theself-commutating transistor device 225 and the second diode 230 areconnected in anti-parallel to form a uni-directional semiconductorswitch.

The self-commutating transistor device 225 can be an insulated-gatebipolar transistor (IGBT). In alternative embodiments, otherself-commutating devices may be used, such as a MOSFET transistor.Collectively, the self-commutating semiconductor switch 220, the firstdiode 235, and the capacitor 240 may be referred to as a commutationmodule. A commutation module may contain different components and ordifferent configurations than shown in the circuit 200, but the circuit200 shows one illustrative embodiment of a commutation module.

In the circuit 200, the capacitor 240 is used as a voltage source forcommutating the SCR 205 off. In alternative embodiments, other voltagesources may be used, such as a battery. A voltage source or, as in thecircuit 200, the capacitor 240 provides a reverse bias voltage to theSCR 205. The capacitor 240 is sized to provide enough voltage forvarious circuit drops plus sufficient voltage to reverse bias to the SCR205. The first diode 235 is also used to provide reverse blocking ofline voltage when the SCR 205 is off. The first diode 235 may be ahigh-voltage diode. Voltage provided by the capacitor 240 may be on theorder of 20-30 volts for smaller devices, and on the order of 30-50volts for larger devices with larger circuit inductances.

In the circuit 200, the capacitor 240 is directly connected to an anodeside of the first diode 235, and the self-commutating semiconductorswitch 220 is directly connected to a cathode side of the first diode235. The input terminal 215 is configured to receive an operatingsignal. The output terminal 210 is in electrical communication with theinput terminal 215 when the static switch is closed. The operatingsignal is provided to a load from the output terminal. The circuit 200may also be utilized in any type of circuit that includes use for aforce commutated SCR.

The circuit 200 as shown connects a silicon-controlled rectifier (SCR)205 and a commutation module in parallel. The commutation moduleincludes a voltage source (the capacitor 240), the diode 235, and theself-commutating semiconductor switch 220. The circuit 200 also connectsa load to an operating signal. The load may be connected to the outputterminal 210, while the operating signal may be connected to the inputterminal 215. Accordingly, when the SCR 205 is turned on, current may bepassed from the input terminal 215 to the load through the SCR 205. TheSCR 205 may be turned off by first removing a gate current and then byapplying, by the commutation module, a reverse bias voltage to the SCR205, and the operating signal may not be connected to the outputterminal 210 and the load. As noted above, applying the reverse biasvoltage to the SCR may include applying a signal to a gate of theself-commutating transistor device 225 in order to apply the reversebias voltage to the SCR 205. The static switch (the SCR 205) is in theclosed position during a normal operating condition such that theoperating signal may pass through the static switch to the outputterminal 210. When the SCR 205 is turned off, the static switch is in anopen position

In another illustrative embodiment, a DC static switch such as thecircuit 200 may also be used for fast disconnects as a solid state DCcircuit breaker. Such a switch could be implemented without the use ofmoving parts, such as those often used in mechanical circuit breakers.For example, a system may include a battery bank connected to aninverter DC bus. Such a system may utilize a near instantaneous turn-offof DC current using a DC static switch, such as the circuit 200.

FIG. 3A is a circuit diagram illustrating a full alternating current(AC) switch utilizing SCRs and IGBTs in accordance with an illustrativeembodiment. In alternative embodiments, fewer, additional, and/ordifferent elements may be present. In a circuit 300, twosilicon-controlled rectifiers (SCRs) 310 and 315 are connected inanti-parallel and form a switch that can be used as an alternatingcurrent (AC) static switch and commutation module in conjunction with avoltage sag or voltage swell correction device. The circuit 300 includestwo commutation modules for the two SCRs 310 and 315. Each of thecommutation modules includes a voltage source (voltage sources 320 and335). Furthermore, each of the commutation modules can share a commonpower supply with each of the SCR 310 and SCR 315 gate drivers. A gatedrive circuit (not pictured here) for the insulated-gate bipolartransistors (IGBTs) 330 and 345 draws very little power because a gatepulse supplied to the IGBTs 330 and 345 may be short in duration andinfrequent. For example, such gate pulses may be on the order of 100 to300 microseconds (ps) at a frequency on the order of AC linefrequencies. In alternative embodiments, other self-commutating devicesthan IGBTs may be used, such as MOSFET transistors.

The circuit 300 includes a first and second commutation module for eachof SCR 310 and SCR 315. The first commutation module includes thevoltage source 320, a diode 325, and a self-commutating semiconductorswitch 330, which are all connected in series. Similarly, the secondcommutation module includes the voltage source 335, a diode 340, and aself-commutating semiconductor switch 345, which are all connected inseries. The SCR 310, the SCR 315, the first commutation module, and thesecond commutation module are all connected in parallel. The voltagesources 320 and 335 may be different types of sources in differentembodiments, such as capacitors or batteries. The first commutationmodule is configured to apply a reverse bias voltage to the SCR 310 toturn off the SCR 310. The second commutation module is configured toapply a reverse bias voltage to the SCR 315 to turn off the SCR 315. Asdiscussed above, the reverse bias voltages used to turn off the SCRs 310and 315 may be on the order of 20-50 volts.

In one embodiment, the circuit 300 may be utilized as an AC staticswitch in a voltage sag or voltage swell correction device. A regulatormodule may also be used in this embodiment to apply a correction signalduring at least a portion of a voltage sag or voltage swell. Theregulator module may be connected to an output terminal 350 to apply thecorrection signal to a load connected to the output terminal 350. Inother various embodiments, a regulator module may also be connected toan input terminal 305, such as those shown in the incorporated referenceU.S. Pat. No. 7,920,392 or FIG. 6 as disclosed herein. During a normaloperating condition, the SCRs 310 and 315 (collectively the AC staticswitch) are on (or in a closed position) allowing AC current to flowthrough the AC static switch. The static switch can be closed byapplying a signal to each of the gates of the SCRs 310 and 315 to makesure that they are active and current can flow through them. In thisway, the regulator module can be bypassed. When a voltage sag or voltageswell is detected by a device controller, the AC static switch isswitched off (the AC static switch is in an open position during atleast a portion of the voltage sag or voltage swell) so that theregulator module is not bypassed by the switch. In this way, acorrection signal may be applied to the output signal 350 during atleast a portion of a voltage sag or voltage swell. In order to turn offthe switch, gate signals of both SCRs are removed immediately before acommutation pulse of the proper time duration is applied the particularconducting SCR. Then the system determines which of the SCRs 310 and 315has current flowing through it. The device controller also determineswhether the sag is happening during a positive current flow or negativecurrent flow of the AC operating signal. In this way, the correctcommutation module can be triggered to supply a pulse to turn off theSCR that is on during the voltage sag or voltage swell. For example, ifa voltage sag or voltage swell occurs during a positive current flow,through SCR 310, the first commutation module should be triggered tosend a pulse to turn off the SCR 310. If a voltage sag or voltage swelloccurs during a negative current flow, through the SCR 315, the secondcommutation module should be triggered to send a pulse to turn off theSCR 315.

In some embodiments, circuit components may be reduced becauseself-commutating semiconductor switches, as well as diodes, may be soldin pairs. FIG. 3B is a circuit diagram illustrating a full alternatingcurrent (AC) switch 301 utilizing paired self-commutating semiconductorswitches and diodes in accordance with an illustrative embodiment. Inalternative embodiments, fewer, additional, and/or different elementsmay be present.

In the circuit 301, a diode pair 360 includes a diode 341 and a diode326. The diode pair may be used, for example, in place of the diodes 325and 340 of FIG. 3A. The circuit 301 also includes a self-commutatingswitch pair 355. The self-commutating switch pair 355 includes aself-commutating switch 346 and a self-commutating switch 331. Theself-commutating switch pair 355 may be used, for example, in place ofthe self-commutating semiconductor switch 345 and the self-commutatingsemiconductor switch 330. Accordingly, in the circuit 301, the diode326, the self-commutating switch 331, and a capacitor 321 can functionas a first commutation module, similar to the first commutation moduledescribed above with respect to FIG. 3A. Similarly, the diode 341, theself-commutating switch 346, and the capacitor 346 can function as asecond commutation module, similar to the second commutation moduledescribed above with respect to FIG. 3A.

FIG. 4 is a circuit diagram illustrating an AC switch utilizing snubbercomponents in accordance with an illustrative embodiment. In alternativeembodiments, fewer, additional, and/or different elements may bepresent. A circuit 400 includes the naturally occurring parasitic lineinductance 415 that may store energy that should be dissipated safelywhen an SCR is commutated off. Accordingly, the circuit 400 includesvarious snubber components which help absorb and dissipate energy storedin the line or load side inductances when an SCR (or AC static switch)is force-commutated off.

The circuit 400 includes similar elements to those shown in FIG. 3A anddiscussed above. The circuit 400 also includes an AC voltage source 410,system commons 405 and 455, and a load 450. As previously mentioned, thecircuit 400 also includes a line (or load) inductance 415. The energystored in the line inductance 415 may be dissipated by snubbercomponents. The resistor-capacitor (RC) snubber components in thecircuit 400 include a resistor 420 and capacitor 425 that are connectedin series, and the whole snubber is connected in parallel with aself-commutating semiconductor switch of the second commutation module.The snubber components in the circuit 400 also include a resistor 430and capacitor 435 that are connected in series, and the whole snubber isconnected in parallel with a self-commutating semiconductor switch ofthe first commutation module. The snubber components in the circuit 400also include a resistor 445 and capacitor 440 that are connected inseries, and the whole snubber is connected in parallel with the ACstatic switch (SCRs). The various snubber components can dissipateenergy trapped in the circuit inductance when the SCRs are commutatedoff. There may be other similar snubber configurations, known to thoseskilled in the art, which may be used to absorb parasitic circuit energywhen the SCRs are commutated off.

At high currents, SCRs may be larger, and inductances in the line arelarger because of greater distances between components in the system. RCsnubbers as disclosed above may not be sufficient to dissipate greaterenergy stored in the circuit. Accordingly, a voltage clamp may beadditionally used.

FIG. 5A is a circuit diagram illustrating circuit 500, an AC switchutilizing a bi-directional voltage clamp 505 in accordance with anillustrative embodiment. In alternative embodiments, fewer, additional,and/or different elements may be present. The circuit 500 includeselements similar to FIGS. 3 and 4, except the RC snubbers are not shown.Further, the circuit 500 includes parasitic line and load inductance515.

The voltage clamp 505 is connected in parallel with the SCRs (AC staticswitch), the first commutation module, and the second commutationmodule. The voltage clamp 505 includes a terminal 510 on a supply sideof the device connected to an anode side of a diode 520 and a cathodeside of a diode 525. The voltage clamp 505 also includes a terminal 515on the load side of the device connected to an anode side of a diode 540and a cathode side of a diode 545. The voltage clamp 505 also includes afirst capacitor/resistor group of capacitor 550 and resistor 555, aswell as a second capacitor/resistor group of capacitor 560 and resistor565. The capacitor and resistor of each group are connected in parallel.A terminal 530 of the voltage clamp 505 is connected to a cathode sideof the diode 520, a cathode side of the diode 540, and the firstcapacitor/resistor group. A terminal 535 of the voltage clamp 505 isconnected to an anode side of the diode 525, an anode side of the diode545, and the second capacitor/resistor group. A terminal 570 of thevoltage clamp 505 is connected to a system common 575, the firstcapacitor/resistor group, and the second capacitor/resistor group.

FIG. 5B is a circuit diagram illustrating an alternative embodiment ofan AC switch utilizing an isolated bi-directional voltage clamp 506 inaccordance with an illustrative embodiment. In alternative embodiments,fewer, additional, and/or different elements may be present. FIG. 5Bshows a circuit 501, which has several similar components to the circuit500 shown in FIG. 5A. However, the circuit 501 includes an isolationtransformer 517 to charge the clamp capacitors. The midpoint of theseries-connected capacitors are not referenced to circuit common incontrast to the midpoint of the capacitors of the voltage clamp 505 inFIG. 5A. The embodiment shown in FIG. 5B of the voltage clamp 506 can beused to implement an AC static switch in a three phase voltage sagcorrector that has no available AC supply common (neutral). In otherwords, depending on the application, the capacitors of a voltage clampmay be referenced differently.

The voltage clamp 506 is connected in parallel with the SCRs (AC staticswitch), the first commutation module, and the second commutationmodule. The voltage clamp 506 includes a terminal 511 on a supply sideof the device connected to an anode side of a diode 521 and a cathodeside of a diode 526. The voltage clamp 506 also includes a terminal 516on the load side of the device connected to an anode side of a diode 541and a cathode side of a diode 546. The voltage clamp 506 also includes acapacitor 585 and resistor 580. The capacitor 585 and the resistor 580are connected in parallel. A terminal 531 of the voltage clamp 506 isconnected to a cathode side of the diode 521, a cathode side of thediode 541, the capacitor 585, and the resistor 580. A terminal 536 ofthe voltage clamp 506 is connected to an anode side of the diode 526, ananode side of the diode 546, the capacitor 585, and the resistor 580.The function of the voltage clamp is to absorb parasitic inductiveenergy in the same manner as the RC snubber referenced earlier. Energyis accumulated in the clamp capacitors in a large pulse as the SCRs arecommutated and then the energy is dissipated more slowly through theparallel resistors.

FIG. 6 is a circuit diagram illustrating a fully integrated three phaseAC static switch with a shunt connected inverter 605 and input rectifier610 accordance with an illustrative embodiment. In alternativeembodiments, fewer, additional, and/or different elements may bepresent. The circuit 600 shows a regulator module with a rectifier 610,a capacitor 615, and an inverter 605. The regulator module can apply acorrection signal to a load 630 at least during a part of a voltage sag.Further, as shown in FIG. 6, where a shunt-connected inverter is on theload side of the AC static switch, a line rectified DC bus circuit mayserve as a voltage clamp to absorb line side inductive energy. Theanti-parallel inverter IGBT diodes and DC bus may also serve as a clampto handle load side inductive energy. In other words, the static switchand inverter can essentially share some common components that providedifferent functions depending on whether the device is in a normaloperating condition (AC static switch closed) or a voltage sag condition(AC static switch open). Although only one static switch is shown forthe first A phase for clarity, a second and third static switch wouldalso be present for the second B phase and the third C phase in anillustrative embodiment.

FIG. 7A is a circuit diagram illustrating an auxiliary commutatedalternating current (AC) static switch circuit with only one IGBT andfour auxiliary SCRs in accordance with an illustrative embodiment. Inalternative embodiments, fewer, additional, and/or different elementsmay be present. IGBTs can be higher cost components of the commutationand switch circuits as disclosed herein. Accordingly, reducing thenumber of IGBTs may lower the cost of the device. A circuit 700 shows anauxiliary commutation circuit that utilizes only one IGBT 735.

The circuit 700 includes an AC static switch of two SCRs 760 and 765connected in anti-parallel. The circuit 700 also includes a commutationmodule connected in parallel with the AC static switch. The commutationmodule includes a terminal 705 on a supply side of the device connectedto an anode of an SCR 710 and a cathode side of an SCR 715. A terminal740 on a load side of the device is connected an anode side of an SCR745 and a cathode side of an SCR 750. A terminal 725 is connected to acathode side of the SCR 710, and a cathode side of the SCR 745, and afirst side of an IGBT 735. A terminal 720 is connected to an anode sideof the SCR 715, and anode side of the SCR 750, and a first side of avoltage source 730. A terminal 755 is connected to a second side of thevoltage source 730 and a second side of the IGBT 735.

To produce a commutation pulse that turns off SCR 760, SCR 710 and SCR750 are gated on along with the IGBT 735. Likewise, SCR 745 and SCR 715are gated on, along with IGBT 735, when turning off SCR 765. Theadditional circuit complexity may use isolated drivers for the variousSCR gate currents; but these can be small transformers driven by acommon pulse driver for the IGBT. The IGBT gate drive and auxiliarycommutation capacitor (730) can also share a common isolated powersupply. The commutating SCRs (710, 715, 745, and 750) are significantlysmaller than the AC switches (SCRs 760 and 765) since they may onlyconduct load current on the order of 100-300 microseconds (ps). Forexample, a 500 Amp (A) SCR may have a 14000 A pulse rating for 10milliseconds. This pulse is sufficient to turn off a current of 8000 Ain the static switch. Additional snubber circuitry, such as a snubber770, is used to protect the IGBT but it may be small in comparison tothe commutating components. The snubber 770 includes a resistor andcapacitor connected across the IGBT 735. The snubber shown is onepossible configuration, other snubber configurations may be used. Thesnubber 770 functions similarly to the snubbers described above withrespect to FIG. 4. A voltage clamp may also be added to this circuit inthe same manner as described earlier.

FIG. 7B is a circuit diagram illustrating an alternative auxiliarycommutated alternating current (AC) static switch circuit with only oneIGBT and four auxiliary SCRs in accordance with an illustrativeembodiment. A circuit 701 is similar to the circuit 700 discussed above,but with different snubber components. For example, instead of thesnubber 770 of the circuit 700, the circuit 701 shows a snubberincluding a resistor 775 and a capacitor 780 connected in parallel. Inaddition, the circuit 701 includes a snubber across the static switchincluding a resistor 785 and a capacitor 790 connected in series.

Advantageously, in the systems and methods disclosed herein, commutationis decoupled from inverter operation (i.e., correction signals beingapplied during at least a portion of a voltage sag or voltage swell).Dynamics associated with parasitic capacitances and inductances betweena shunt-connected inverter and an SCR static switch may not affecteither the commutation process or an inverter transient response.Another advantage is that commutation time may be consistent regardlessof circuit impedances that vary from application to application.Commutation time can also be as fast as in a series dynamic sagcorrection topology. Commutation can also be more reliable in thepresent systems because a commutating voltage is independent of voltagesand circuit conditions with regard to operating signals and differentloads.

FIG. 8 is a graph illustrating simulated voltage results of an auxiliarycommutated SCR circuit in an AC static switch configuration deliveringpower to a resistive load without a voltage clamp in accordance with anillustrative embodiment. In alternative embodiments, fewer, additional,and/or different elements may be present. A line 805 shows input voltageinto the device, with a significant inductive spike when the SCR isturned off. A line 810 shows the output voltage of the device whencoupled to a shunt-connected inverter configuration, such as shown inFIG. 6. Note that even where the SCR is turned off, there is no largevoltage spike in the output.

FIG. 9 is a graph illustrating simulated current results of an auxiliarycommutated SCR circuit in an AC static switch configuration deliveringpower to a resistive load without a voltage clamp in accordance with anillustrative embodiment. In alternative embodiments, fewer, additional,and/or different elements may be present. FIG. 9 corresponds with FIG.8. A line 905 corresponds to current from the AC supply flowing throughthe static switch and through the load. A line 910 corresponds to an SCROFF command. Note that the load current goes to zero just after the SCROFF command is initiated demonstrating SCR commutation at a non-zerocurrent.

FIG. 10 is a graph illustrating laboratory results of an auxiliarycommutated SCR circuit in an AC static switch configuration deliveringpower to a resistive load without a voltage clamp in accordance with anillustrative embodiment. In alternative embodiments, fewer, additional,and/or different elements may be present. FIG. 10 shows similar data toFIGS. 8 and 9, but is measured, as opposed to simulated, data. A line1005 shows input voltage with a voltage spike. A line 1010 shows outputvoltage of the device, when coupled to a shunt-connected inverterconfiguration, such as shown in FIG. 6, without a large voltage spike. Aline 1015 shows the circuit current, and a line 1020 shows the SCR OFFcommand. Note that the load current goes to zero just after the SCR OFFcommand is initiated demonstrating SCR commutation at a non-zerocurrent.

FIG. 11 is a graph illustrating simulated voltage results of anauxiliary commutated SCR circuit in an AC static switch configurationdelivering power to a resistive load with a voltage clamp (e.g., thevoltage clamp of FIG. 5A or 5B) in accordance with an illustrativeembodiment. In alternative embodiments, fewer, additional, and/ordifferent elements may be present. FIG. 11 is similar to FIG. 8, butshows simulated results with a voltage clamp. Accordingly, a spike on aninput voltage line 1105 is very small compared to the spike in the line805, because a voltage clamp is present to absorb and dissipate theinductive energy when the SCR is turned off. A line 1110 shows minimalspike on the output voltage as well.

FIG. 12 is a graph illustrating simulated current results of anauxiliary commutated SCR circuit in an AC static switch configurationdelivering power to a resistive load with a voltage clamp in accordancewith an illustrative embodiment. In alternative embodiments, fewer,additional, and/or different elements may be present. A line 1215 showsthe current from the AC supply flowing through the static switch andthrough the load. A line 1220 shows the SCR OFF command. Note that theload current goes to zero just after the SCR OFF command is initiateddemonstrating SCR commutation at a non-zero current.

FIG. 13 is a graph illustrating laboratory results of an auxiliarycommutated SCR circuit in an AC static switch configuration deliveringpower to a resistive load with a voltage clamp in accordance with anillustrative embodiment. In alternative embodiments, fewer, additional,and/or different elements may be present. A line 1305 shows the inputvoltage into a device. A line 1310 shows the output voltage from adevice when coupled to a shunt-connected inverter configuration such asFIG. 6. A line 1315 shows circuit current in the device. A line 1320shows the SCR OFF command. Note that the load current goes to zero justafter the SCR OFF command is initiated demonstrating SCR commutation ata non-zero current. As in FIGS. 11 and 12, FIG. 13 shows that, with avoltage clamp, voltage spikes on the input line voltage from lineinductance can be significantly reduced to prevent damage to thecircuitry of a voltage sag or voltage swell correction device and load.

FIG. 14 is a circuit diagram illustrating simplified feedback elementsof an auxiliary commutated SCR circuit control in accordance with anillustrative embodiment. In alternative embodiments, fewer, additional,and/or different elements may be present. The circuit 1400 includes anAC static switch 1410 and a commutation module 1405. The circuit 1400shows a node 1425 that can measure current through the AC static switch.The circuit 1400 also includes a voltage sensor 1415, an absolute valueblock 1420, and a comparator 1430. The circuit 1400 further includes acurrent polarity detector comparators 1435, 1440, 1445, and 1450.

FIG. 15 is a flow chart illustrating an auxiliary commutated SCR circuitcontrol process in accordance with an illustrative embodiment. Inalternative embodiments, fewer, additional, and/or different operationsmay be performed. Also, the use of a flow diagram is not meant to belimiting with respect to the order of operations performed. The controlstate flow chart in FIG. 15 is described below along with the circuit1400 in FIG. 14. The operations of FIG. 15 correspond to control paths.That is, when an operation between blocks occurs in FIG. 15, the controlsystem is reacting to a certain state of the circuit and controlling thecircuit according to the control paths or operations accordingly asdescribed below.

The various elements in the circuit 1400 demonstrate basic auxiliarycommutation control function for an AC static switch. In the Normal_Onblock 1505, the SCR gates in the AC static switch 1410 are provided withcontinuous current pulses to keep the device active. An SCR OFF commandmay be asserted at an operation 1510 which sends the controller to theGates Off state at a block 1515. In this state, the gate current isremoved from the SCRs in the AC static switch 1410. However, sincecurrent may be generally still flowing through the SCRs (the AC staticswitch 1410 has not commutated), the AC static switch 1410 may notnecessarily stop conducting at this point. Accordingly, the SCRs may beforce-commutated off to ensure that the AC static switch 1410 is off.Four measurable SCR current/voltage conditions are possible: 1) positivecurrent is flowing through a first SCR and the static switch voltage ispositive and low; 2) negative current is flowing through a second SCRand the static switch voltage is negative and low; 3) both SCRs are off,no current is flowing and the SCR voltage is positive or negative andhigh (SCRs are off); 4) the SCR current is zero after a naturalcommutation or below the current polarity detector threshold, but theSCR voltage is too low to indicate whether or not the SCR is off.

When condition 1 is met, the “Ipos_set” comparator 1435 signal isactive. In other words, the comparator 1435 indicates that a positivecurrent is above a noise threshold (as compared to a reference current).The “Ipos_set” signal causes an operation 1520 in FIG. 15 to advance thecontrol state to a positive ready block 1525. At the positive readyblock 1525, the system is ready to send a commutation pulse to turn offthe first SCR. After a sufficient delay time to insure thenon-conducting SCR has no current reapplied before its turn-off time hasexpired, an operation 1535 advances the control state to a positivepulse block 1540, where the positive commutation pulse is applied. Afterthe pulse is applied for the turn off time of the SCR, line 1545advances the controller to the Off Wait state 1548. Momentarily, theSCR_is_off signal from comparator 1430 should go high indicating the SCRwas successfully commutated (operation 1552) and the controller advancesto the Normal_Off state 1553. If, for some reason, the SCR does not shutoff, the system waits another much longer amount of time, such as 11milliseconds (greater than 10 milliseconds, the amount of time needed ina 50/60 Hertz (Hz) AC system for the current to cross zero and ensurethat the SCRs naturally commutate). After the wait time passes(operation 1552) the controller will advance to the Normal_off state1553. When it is desired to turn the SCRs back on, operation 1554advances the controller to the Normal_On block 1505, where the SCR gatesin the AC static switch 1410 are again provided with continuous currentpulses to keep the device active.

When condition 2 is met, the “Ineg_set” comparator 1440 signal isactive. In other words, the comparator 1440 indicates that a negativecurrent is above a noise threshold (as compared to a reference current).The “Ineg_set” signal causes an operation 1570 in FIG. 15 to advance thecontrol state to a negative ready block 1575. At the negative readyblock 1575, the system is ready to send a commutation pulse to turn offthe second SCR. After a sufficient delay time to insure thenon-conducting SCR has no current reapplied before its turn-off time hasexpired, an operation 1585 advances the control state to a negativepulse block 1590, where the negative commutation pulse is applied. Afterthe pulse is applied for the turn off time of the SCR, line 1595advances the controller to the Off Wait state 1548. Momentarily, theSCR_is_off signal from comparator 1430 should go high indicating the SCRwas successfully commutated (operation 1552) and the controller advancesto the Normal_Off state 1553. If for some reason, the SCR does not shutoff, the system waits another much longer amount of time, such as 11milliseconds (greater than 10 milliseconds, the amount of time needed ina 50/60 Hertz (Hz) AC system for the current to cross zero and ensurethat the SCRs naturally commutate. After the wait time passes (operation1552) the controller will advance to the Normal_off state 1553. When itis desired to turn the SCRs back on, operation 1554 advances thecontroller to the Normal_On block 1505, where the SCR gates in the ACstatic switch 1410 are again provided with continuous current to keepthe device active.

When condition 3 is met, the “SCR_is_off” comparator 1430 is active. Inthis scenario, the SCRs have turned off naturally without needing acommutation signal. The “SCR_is_off” signal goes high because there issignificant voltage detected across the AC static switch. This causes anoperation 1550 to advance the control state to a ready wait block 1555.At the block 1555, the system will wait a certain amount of time beforean operation 1565 advances the control state to an off wait state block1548. The amount of time may be the maximum amount of time it would takefor an SCR to fully turn off, such as 200 ps. If the “SCR_is_off” signalfrom comparator 1430 goes inactive during the time the system is atstate block 1555, the system will perform an operation 1560 and returnto the state block 1515. Since the SCR_is_off signal from comparator1430 is already high indicating the SCR was successfully commutated(operation 1552) the controller should immediately advance to theNormal_Off state 1553. If for some reason, the SCR_is_off signal hasgone inactive, the system waits another much longer amount of time, suchas 11 milliseconds (greater than 10 milliseconds, the amount of timeneeded in a 50/60 Hertz (Hz) AC system for the current to cross zero andensure that the SCRs naturally commutate. After the wait time passes(operation 1552) the controller will advance to the Normal_off state1553. When it is desired to turn the SCRs back on, operation 1554advances the controller to the Normal_On block 1505, where the SCR gatesin the AC static switch 1410 are again provided with continuous currentto keep the device active.

If conditions 1, 2, or 3 do not occur after a waiting period such as 22milliseconds for example, condition 4 is implied. Once the waitingperiod transpires, an operation 1517 advances the controller to thestate to the Normal_Off state block 1553. When it is desired to turn theSCRs back on, operation 1554 advances the controller to the Normal_Onblock 1505, where the SCR gates in the AC static switch 1410 are againprovided with continuous current to keep the device active.

As noted above, if condition 1 is met the controller knows that anauxiliary commutation voltage should be applied in the direction ofreverse biasing the first SCR and advances to state “Pos Ready” at stateblock 1525. If condition 2 is met, the controller moves to “Neg Ready”at state block 1575 to prepare to reverse bias for the second SCR. Ifcondition 3 is met, the SCRs are already off or have naturallycommutated and do not require an auxiliary commutation and thecontroller advances to “Ready Wait” at state block 1555.

The first three cases, the conditions 1, 2, or 3, must persist for theTq time of the particular SCRs used (e.g., 200 ps) to insure that thenon-conducting SCR has been non-conducting for the Tq time, i.e., thetime interval required after forward current has decreased to zero forthe specific SCR device to recover capability to block its ratedvoltage. If this time condition has not been met, the non-conducting SCRmay turn back on when the auxiliary commutation voltage is appliedbecause it would see a forward bias before it is completely off.

For example, given an AC current in the static switch, assume the secondSCR had been conducting current, and that both the first and second SCRshad been provided with continuous gate current, just prior to thecommand to turn off the SCRs. Then, further assume that the AC currentin the static switch passes through zero and the first SCR just startsto conduct. Finally, assume that the SCR off command is asserted at atime less than its Tq time after the second SCR stopped conducting. Inthis case, the Ipos_set signal from comparator 1435 goes high indicatinga positive commutation voltage should be applied. If acted uponimmediately, the IGBT and auxiliary SCRs would be gated on to apply thecommutation voltage needed to reverse bias the first SCR. However, atthe same time, the second SCR would be forward biased by that samecommutation voltage. Since the second SCR cannot block forward voltageuntil its Tq time has elapsed, the second SCR may begin conductingresulting in a short circuit of the commutation circuit. Very largecurrents may flow through the second SCR resulting in potential circuitdamage or minimally, delayed static switch commutation.

As explained above, in each of the “Ready” states (positive, negative,and ready wait), the circuit should remain in a stable state for the Tqtime (e.g., 200 ps) before the commutation pulse is actually applied. Ifthe current direction changes or the “SCR_is_off” status changes withinthe Tq time, the controller reverts back to the “Gates Off” state untilanother circuit condition drives it to one of the “Ready” states for astable amount of time. For example, at an operation 1580, an “Ineg_rst”signal from the comparator 1450 is active causing the system to revertto gates off state block 1515. In another example, at an operation 1530,an “Ipos_rst” signal from the comparator 1445 is active causing thesystem to revert to gates off state block 1515.

Given a stable “Pos Ready” or “Neg Ready” state at state blocks 1525 or1575, respectively, the controller will advance to the respective “PosPulse” or “Neg Pulse” state blocks 1540 or 1590 with operations 1535 or1585 respectively, and apply the required commutation pulse polarity byturning on the IGBT and the appropriate auxiliary SCRs for an additionaltime period of Tq. This is to ensure that the device being commutatedhas sufficient time to turn off completely while reversed biased by theauxiliary commutation pulse. If the SCR current is not high enough totrigger the “Ipos_set” or “Ineg_set” comparators and advance to stateblocks 1525 or 1575, the SCRs will eventually naturally commutate as theAC current passes through zero, and subsequent AC circuit voltage willtrigger the “SCR_is_off” comparator and advance the controller to “ReadyWait” state block 1555.

If the SCRs turn off but the circuit voltage is too low to trigger the“SCR_is_off” comparator, the controller has a time out condition whichforces an exit of the “Gates Off” state at state block 1515. The timeoutperiod may, for example, be set at 22 milliseconds under the assumptionthat in a 50/60 Hz AC circuit, the current will cross zero and naturallycommutate in both directions in no more than 20 ms. The time outfunction will allow the controller to exit the “Gates Off” state ifcircuit currents and voltages are uncharacteristically low. Such a timeout will activate an operation 1517 and take the system back to theNormal_Off state block 1553.

If the controller has not timed out as described above, it mayunconditionally advance to the “Off Wait” state 1548 after the Tq time.Typically the “SCR_is_off” comparator signals immediately after thecommutation pulse and the controller exits the “Off Wait” statesignifying the end of the commutation cycle. If for some reason, thecommutation failed or the circuit voltage is too low to indicate the SCRis off, there is another time out condition, for example an 11 ms timeout condition, that allows the controller to exit the state 1548 (underthe same assumption above that a natural commutation will have occurredwithin 10 ms or less).

FIG. 16 is a circuit diagram illustrating a dynamic brake for anauxiliary commutated SCR circuit in accordance with an illustrativeembodiment. In alternative embodiments, fewer, additional, and/ordifferent elements may be present. The circuit 1600 shows a dynamicbrake power circuit 1610 that can be used to dissipate energy from thevoltage clamp, a direct current (DC) bus 1620 is charged by parasiticinductive energy represented by a current source 1615. The energydissipated can be turned into heat by a dynamic brake. Since the dynamicbrake dissipates energy in conjunction with the voltage clamp, lowercapacitances may be used in the voltage clamp circuit. The dynamic brakepower circuit 1610 can be shut on and off based on voltage hysteresis asshown in the dynamic brake control block 1605.

In another illustrative embodiment, auxiliary commutated SCR technologymay be utilized in voltage sag testing in which a voltage sag isgenerated by switching from nominal line voltage to a reduced voltagetap on a transformer. Contactor-based switching voltage sag generatorsmay be slow, with long open transitions (exceeding one cycle) betweentap changes. These types of testers may switch at random phase anglesbut the particular angle is unpredictable, which may be undesirable. Saggenerators that use SCRs in an AC static switch configuration may haveshorter open transitions but may only switch at current zeros and alsonot perform phase-angle control. An auxiliary commutated solution mayprovide a predictable turn-off time for phase angle control and allowthe tap-changing open transition dead time to be significantly reduced.For example, auxiliary commutated SCR AC static switches may be usedwith different sources to control exactly when a signal applied to aload is switched to a different source. In another embodiment, multipleauxiliary commutated SCR static switches may tap a transformer indifferent locations, therefore allowing a quick switch between locationsof drawing a signal from a transformer. Such embodiments may offeradvantages in voltage sag testing.

In an illustrative embodiment, any of the operations described hereinincluding a controller can be implemented at least in part ascomputer-readable instructions stored on a computer-readable medium ormemory. Upon execution of the computer-readable instructions by aprocessor, the computer-readable instructions can cause a computingdevice to perform the operations.

The foregoing description of illustrative embodiments has been presentedfor purposes of illustration and of description. It is not intended tobe exhaustive or limiting with respect to the precise form disclosed,and modifications and variations are possible in light of the aboveteachings or may be acquired from practice of the disclosed embodiments.It is intended that the scope of the invention be defined by the claimsappended hereto and their equivalents.

What is claimed is:
 1. A device comprising: a first silicon-controlledrectifier (SCR); and a first commutation module comprising a firstvoltage source, a first diode, and a first self-commutatingsemiconductor switch, wherein: the first voltage source, the firstdiode, and the first self-commutating semiconductor switch of the firstcommutation module are connected in series, the first SCR is connectedin parallel to the first commutation module, and the first commutationmodule is configured to apply a first reverse bias voltage to the firstSCR to turn off the first SCR.
 2. The device of claim 1, wherein thefirst self-commutating semiconductor switch comprises a firstself-commutating transistor device and a second diode connected inanti-parallel.
 3. The device of claim 1, further comprising: an inputterminal configured to receive a first operating signal; and an outputterminal in electrical communication with the input terminal and throughwhich the first operating signal is provided to a load.
 4. The device ofclaim 3, further comprising: a second silicon-controlled rectifier (SCR)connected in anti-parallel with the first SCR; and a second commutationmodule comprising a second voltage source, a second diode, and a secondself-commutating semiconductor switch, wherein: the second voltagesource, the second diode, and the second self-commutating semiconductorswitch of the second commutation module are connected in series, thefirst SCR, the second SCR, the first commutation module, and the secondcommutation module are connected in parallel, and the second commutationmodule is configured to apply a second reverse bias voltage to thesecond SCR to turn off the second SCR.
 5. The device of claim 4, furthercomprising: a regulator module configured to generate a correctionsignal during at least a portion of a voltage sag or voltage swell; andan alternating current (AC) static switch in electrical communicationwith the input terminal and the output terminal, wherein: the AC staticswitch comprises the first SCR, the second SCR, the first commutationmodule, and the second commutation module, the regulator module isconnected to the output terminal, the AC static switch is in a closedposition during a normal operating condition such that the regulatormodule is bypassed, and the AC static switch is in an open positionduring at least a portion of the voltage sag or voltage swell such thatthe regulator module is not bypassed.
 6. The device of claim 5, furthercomprising a device controller configured to detect the voltage sag orvoltage swell.
 7. The device of claim 4, wherein: the firstself-commutating semiconductor switch and the second self-commutatingsemiconductor switch are a self-commutating semiconductor switch pair;and the first diode and the second diode are a diode pair.
 8. The deviceof claim 4, wherein the first self-commutating semiconductor switchcomprises a first self-commutating transistor device and a third diodeconnected in anti-parallel, and the second self-commutatingsemiconductor switch comprises a second self-commutating transistordevice and a fourth diode connected in anti-parallel.
 9. The device ofclaim 4, further comprising a snubber configured to dissipate energywhen the first SCR or the second SCR are turned off.
 10. The device ofclaim 9, wherein the snubber is connected in parallel with the firstself-commutating semiconductor, the second self-commutatingsemiconductor switch, the first SCR, or the second SCR.
 11. The deviceof claim 9, wherein the snubber comprises a resistance and capacitanceconnected in series.
 12. The device of claim 4, further comprising avoltage clamp configured to dissipate energy when the first SCR or thesecond SCR are turned off, wherein the voltage clamp references a systemcommon or an alternating current (AC) source common.
 13. The device ofclaim 12, further comprising a dynamic brake configured to dissipateenergy from the voltage clamp.
 14. A method comprising: connecting afirst silicon-controlled rectifier (SCR) and a commutation module inparallel; connecting a load to an operating signal; passing theoperating signal through the SCR to the load; and applying, by thecommutation module, a reverse bias voltage to the first SCR to turn offthe first SCR.
 15. The method of claim 14, further comprising:connecting an alternating current (AC) static switch and a commutationmodule in parallel, wherein the AC static switch comprises the first SCRand a second silicon-controlled rectifier (SCR) connected inanti-parallel; connecting the load to the operating signal through theAC static switch during a normal operating condition, wherein the ACstatic switch is in a closed position during the normal operatingcondition; detecting, by a controller, a voltage sag or voltage swell;and applying the reverse bias voltage to the first SCR or the second SCRof the AC static switch, wherein the AC static switch is in an openposition during at least a portion of the voltage sag or voltage swell,and further wherein the reverse bias voltage turns off the first SCR orthe second SCR.
 16. The method of claim 15, further comprising:connecting a regulator module to the output terminal, wherein during thenormal operating condition the regulator module is bypassed; generating,by the regulator module, a correction signal during at least a portionof the voltage sag or voltage swell; switching the AC static switch tothe open position by applying the reverse bias voltage to the AC staticswitch to turn off the first SCR or the second SCR depending on which ofthe first SCR or the second SCR is conducting current at a time of saidswitching the AC static switch to the open position; and applying thecorrection signal to the operating signal during at least a portion ofthe voltage sag or voltage swell, wherein the correction signal isapplied when the AC static switch is in the open position such that theregulator module is not bypassed.
 17. The method of claim 15, whereinthe commutation module comprises a first self-commutating semiconductorswitch configured to turn off the first SCR and a secondself-commutating semiconductor switch configured to turn off the secondSCR, and wherein the method further comprises: applying a first gatesignal to the first self-commutating semiconductor switch such that thereverse bias voltage is applied to the first SCR; and applying a secondgate signal to the second self-commutating semiconductor switch suchthat the reverse bias voltage is applied to the second SCR.
 18. Themethod of claim 15, wherein the commutation module comprises aself-commutating semiconductor switch, a third silicon-controlledrectifier (SCR), a fourth silicon-controlled rectifier (SCR), a fifthsilicon-controlled rectifier (SCR), and a sixth silicon-controlledrectifier (SCR), wherein the method further comprises: applying a firstgate signal to the self-commutating semiconductor switch, the third SCR,and the sixth SCR such that the reverse bias voltage is applied to thefirst SCR; and applying a second gate signal to the self-commutatingsemiconductor switch, the fourth SCR, and the fifth SCR such that thereverse bias voltage is applied to the second SCR.
 19. A devicecomprising: a first silicon-controlled rectifier (SCR) and a secondsilicon-controlled rectifier (SCR) connected in anti-parallel; and acommutation module connected in parallel with the first SCR and thesecond SCR, wherein the commutation module comprises: a first terminalon a supply side of the device connected to an anode side of a thirdsilicon-controlled rectifier (SCR) and a cathode side of a fourthsilicon-controlled rectifier (SCR); a second terminal on a load side ofthe device connected to an anode side of a fifth silicon-controlledrectifier (SCR) and a cathode side of a sixth silicon-controlledrectifier (SCR); a third terminal connected to a cathode side of thethird SCR, a cathode side of the fifth SCR, and a first side of anself-commutating semiconductor switch; a fourth terminal connected to ananode side of the fourth SCR, an anode side of the sixth SCR, and afirst side of a voltage source; and a fifth terminal connected to asecond side of the self-commutating semiconductor switch and a secondside of the voltage source.
 20. The device of claim 19, furthercomprising: an input terminal configured to receive a first operatingsignal; an output terminal in electrical communication with the inputterminal and through which the first operating signal is provided to aload; a regulator module configured to generate a correction signalduring at least a portion of a voltage sag or voltage swell; and analternating current (AC) static switch in electrical communication withthe input terminal and the output terminal, wherein: the AC staticswitch comprises the first SCR, the second SCR, and the commutationmodule, the regulator module is connected to the output terminal, the ACstatic switch is in a closed position during a normal operatingcondition such that the regulator module is bypassed, and the AC staticswitch is in an open position during at least a portion of the voltagesag or voltage swell such that the regulator module is not bypassed.